EDWARD'S LECTURE NOTES:
More notes at http://tanguay.info/learntracker
C O U R S E
From the Big Bang to Dark Energy
Hitoshi Murayama, University of Tokyo
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C O U R S E L E C T U R E The Milky Way and Its Black Hole Notes taken on March 8, 2016 by Edward Tanguay |
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as you look far away in the universe, you are looking into the past
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International Space Station
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only very recent that humans have developed technology to have a station outside the earth
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floating above the Earth at an altitude of 375 kilometers
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the diameter of the Earth is 12,000 kilometers
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suggests that moving out away from the Earth is not a very easy thing to do
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travel to the moon
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384,400 kilometers
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Kaguya
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nickname for SELENE (Selenological and Engineering Explorer)
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launched on September 14, 2007
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picture:
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went to the other side of the moon
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took pictures of Earth rise
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because distances are so large in space, we use time to describe how far away objects are
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light takes 1.3 seconds to reach the Moon
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Moon is 1.3 light-seconds away
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the Apollo astronauts put a mirror on the Moon
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we can shoot a laser to it and it returns 2.6 seconds later
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Sun
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1.5 10^8 kilometers away
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8.3 light-minutes away
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Hayabusa
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an unmanned spacecraft developed by the Japan Aerospace Exploration Agency (JAXA) which returned a sample of material from a small near-Earth asteroid named 25143 Itokawa to Earth for further analysis
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20 light-minutes away from the Earth (more than two times the distance to the Sun)
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the command sent to the probe to deploy the Minerva lander arrived to late, since it took 20 minutes to get there
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there is a 40-minute lag for making decisions of how the probe should interact with its environment
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it had to decide as much as it could on its own
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Neptune
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four light-hours away
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Voyager
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human-made object that is the farthest from Earth
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16-light-hours away
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we are still communicating with it
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closest star
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Proxima Centauri
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4.2 light-years
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Voyager will have to travel for over 10,000 years to get to Proxima Centauri
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Milky Way galaxy
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we are in a galaxy which is a disc and when we look at the Milky Way we see the disc from the inside
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we are 28,000 light-years away from the center of the galaxy
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it's only 1500 light-years thick
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our solar system is revolving around the center of the our galaxy
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at a speed of 220 km/s
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something is pulling us to the center of the galaxy
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we know this to be a black hole
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with infrared light we can see through the dust and debris in space to see the motion of stars at the center of the galaxy
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something is pulling a star, and after it passes through, it speeds on quickly
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it takes 20 years for a star to orbit around this very heavy object
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by studying the motion of these stars, you can determine how massive the object is
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the answer is staggering: the object in the middle of the Milky Way galaxy is four million times heavier than our Sun
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nothing can be that heavy except for a black hole
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black hole at center of the Milky Way
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four million times our solar mass
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other galaxies have heavier black holes
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it can consume objects including gas around it
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even the speed of light is not enough to escape the force of gravity from the black hole
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just before gas enters the black hole, it flashes in light